The present invention relates to a chemical process. More particularly, the present invention relates to a novel process for preparing allylic (2-propenyl) addition products of malonic acid (methane dicarboxylic acid) esters and nitriles that provides unique selectivity to the desired .alpha.-dimethyl malonic acid derivative.
In U.S. Pat. No. 4,257,957, there is provided a process for preparing pyrethroid starting reactants, especially 2(2,2-dichloroethenyl)-3,3-dimethylcyclopropane carboxylates. More particularly, such compounds were derived from (1,1-dimethyl-2-propenyl)malonates or (1,1-dimethyl-2-propenyl)malononitriles. Such starting reactants were in turn prepared by the palladium catalyzed hydrogenation of acetylenic compounds.
N. R. Easton et al., J. Org. Chem., 27, 3602 (1962), disclosed the process for preparing such acetylenic compounds by alkylation of sodiomalonates with acetylenic halides and subsequently partially hydrogenating the resulting product. The process is not readily adapted to commercial practice due to a lack of ready availability of the starting reactants.
J. P. Genet et al, Tetrahedron Lett., 21, 3183-3185 (1980), reported the palladium catalyzed addition of a sterically hindered allylic radical to sodiomalonate esters and observed the unexpected regio- and stereoselectivity of the process to prepare primarily the product resulting from addition of the tertiary-substituted alkyl group. The authors concluded that this selectivity in product formation is due to steric hindrance at the neopentyl-substituted secondary center which directs the reaction towards the tertiary center.
In U.S. Pat. No. 4,362,670, one of the present inventors disclosed the general method of allyl group addition to carbon acids by the use of palladium catalyzed addition of allyl carbonates. The present invention in one embodiment constitutes a special adaption of this process in order to provide unique regio- and stereoselectivity in product distribution to provide addition at tertiary carbon centers of substituted allyl reactants.
A further embodiment of the present invention lies in the discovery that the reaction product of the present process may be employed without purification to remove isomeric by-products in a free radical initiated reaction with tetrahalomethane to prepare trihalomethyl-substituted malonic acid derivatives.
In a further embodiment of the present invention, there is provided a facile process for preparing 3(2,2-dichlorovinyl)-2,2-dimethyl-1-cyclopropane carboxylic acid and esters thereof in relatively high yields starting from freely available starting reactants.